Numerous types of mufflers having various parts and elements for sound suppression or attenuation are known. Nevertheless, slight changes in configuration of elements cause different interference patterns of sound waves of the same and different frequencies. Thus, the art continues to develop since better or approximately equivalent sound suppression results may be obtained with assembly configurations somewhat different from or processes less costly than previous configurations or processes. It is in this sense that the present invention assumes significance relative to the art, and, in this regard, the discussion hereinafter traces improvements in muffler apparatus to show the significance of the present invention.
Rowley (U.S. Pat. No. 3,672,464) shows a muffler having aligned input and output tubes within a housing. A plurality of baffles extends between the tubes and a housing. The output tube is formed to converge from a cylindrical shape to a throat before expanding rapidly outwardly to approximately the earlier indicated cylindrical shape as the output tube is viewed from downstream to upstream. Wagner (U.S. Pat. No. 4,267,899) shows variations on the design to include an offsetting alignment between input and output tubes. Wagner (U.S. Pat. No. 4,368,799) shows further variations which include throat portions in both the input and output tubes. In addition, the mufflers shown in each of these patents include a cylindrical tube encircling the converging and throat portions of the tubes. Thus, it is clear that the manufacturing process requires a forming step, as well as a step for pressing one tube into the other, and a step for pressing on baffles, each step of course adding to manufacturing costs.
Schmeichel (Ser. No. 505,424, filed June 16, 1983, and assigned to the same assignee as the previously mentioned patents) discloses muffler apparatus also having aligned input and output tubes with a converging portion and a throat portion in the output tube. Schmeichel, however, found advantage in forming the converging and throat portion of the output tube to include a plurality of bypass passages which were not constricted. Although such an output tube accomplishes advantageous sound suppression results, it requires the manufacture of the specially shaped tube. For use in a muffler, baffles are then thereafter pressed onto the tube.
The present invention achieves the sound suppression results of the art, but does so with a much more simply manufactured apparatus and, consequently, is less costly.